Seakeeping Constderattons tn a Total Destgn Methodology 
E.H. P. Calculations 
The Effective Horse Power (EHP) of a ship operating in the 
seaway is computed in the following manner. 
First, the bare hull calm water Effective Horse Power is 
computed as a function of ship speed from Reference 4 . This es- 
timate is then augmented by 3% to account for the presence of ap- 
pendages. Second, the Effective Horse Power necessary to overcome 
the increased resistance because of fouling is computed. It is assum- 
ed that the ship is dry docked every year. From the results reported 
in Reference 8 it is found that increasing the value of ACF by 
0.00015 would account, on the average, for the yearly increase of 
resistance due to fouling. Therefore : 
3 
0.00015*pxV »* (1. 6889)° * wetted surface 
P ; = 
fouling 2.* 550 
where V = ship's speed in knots 
3 
sea water density in slugs/t. 
and p 
Third, the wind resistance is computed as a function of the ship 
speed and sea state (H!3 ). From Reference 9 the Effective Horse 
Power necessary to overcome the wind resistance is given by 
2 
0. 00435 *B * Rae 
BS andi 2 * 325, 66 
where B = ship's beam in ft. 
VR = wind velocity relative to the ship in knots. 
The wind velocity relative to the ship, VR, is computed by adding the 
wind speed corresponding to each sea state to the ship's speed V. The 
wind speed as a function of sea state (H'/3) is determined from Fig. 2. 
PS 
